[test-suite] Update test-suite microbenchmarks to use JSON (fix bug 41327)

[homerdin]

Summary

Google benchmark is hoping to drop the CSV output format. This updates the microbenchmark module to use the JSON output.

This fixes PR41327

[lebedev.ri]

Looks good to me.

[lebedev.ri]

Was committed as rT357704, but Differential Revision: prefix was missing.

litsupport/modules/microbenchmark.py

 '''Test module to collect google benchmark results.'''
 from litsupport import shellcommand
 from litsupport import testplan
-import csv
+import json
 import lit.Test
 
 
 def _mutateCommandLine(context, commandline):
     cmd = shellcommand.parse(commandline)
-    cmd.arguments.append("--benchmark_format=csv")
+    cmd.arguments.append("--benchmark_format=json")
     # We need stdout outself to get the benchmark csv data.
     if cmd.stdout is not None:
         raise Exception("Rerouting stdout not allowed for microbenchmarks")
-    benchfile = context.tmpBase + '.bench.csv'
+    benchfile = context.tmpBase + '.bench.json'
     cmd.stdout = benchfile
     context.microbenchfiles.append(benchfile)
 
     return cmd.toCommandline()
 
 
 def _mutateScript(context, script):
     return testplan.mutateScript(context, script, _mutateCommandLine)
 
 
 def _collectMicrobenchmarkTime(context, microbenchfiles):
     for f in microbenchfiles:
         content = context.read_result_file(context, f)
-        lines = csv.reader(content.splitlines())
-        # First line: "name,iterations,real_time,cpu_time,time_unit..."
-        for line in lines:
-            if line[0] == 'name':
-                continue
+        data = json.loads(content)
+
+        # Create a micro_result for each benchmark
+        for benchmark in data['benchmarks']:
             # Name for MicroBenchmark
-            name = line[0]
+            name = benchmark['name']
+
             # Create Result object with PASS
             microBenchmark = lit.Test.Result(lit.Test.PASS)
 
-            # Index 3 is cpu_time
-            exec_time_metric = lit.Test.toMetricValue(float(line[3]))
+            # Add the exec_time metric for this result
+            exec_time_metric = lit.Test.toMetricValue(benchmark['cpu_time'])
             microBenchmark.addMetric('exec_time', exec_time_metric)
 
             # Add Micro Result
             context.micro_results[name] = microBenchmark
 
     # returning the number of microbenchmarks collected as a metric for the
     # base test
     return ({